The present invention relates to a method of forming an electrical connecting structure on an electrode protruding from the surface of an electronic component, e.g., a semiconductor chip.
Flip-chip attachment, where the chip""s input/output terminals are positioned face down on a substrate, has been widely used to join such chips to various substrates, e.g., a printed circuit board. Utilizing this technique, solder or other metal (e.g., copper) bumps are formed on the chip""s input/out terminals to form the electrical connection between the terminals and substrate conductors (e.g., pads).
Because of the recent miniaturization of circuit components (including chips), electrical connecting structures to be formed on the electrodes of an electronic component are getting smaller, and spaced on a narrower pitch (greater density). Such electrical connecting structures may be formed by a transfer method in which solders protrude from the surface of a transfer plate and are transferred to an electronic component. See published Japanese Patent Application No. H01-5039.
A transfer plate can also be used for joining low melting point solder to an electrode pad on a substrate. See U.S. Pat. No. 5,233,504. Another solder plate used to form solder bumps on a substrate is described and illustrated in U.S. Pat. Nos. 5,658,827 and 6,030,889.
Where a single metal bump such as a copper bump is used, solder has been applied to the bump by methods such as plating, vapor evaporation, sputtering deposition or the like. However, such a method requires special equipment and involves several complicated steps, thus necessitating increased production times and costs. The published Japanese Patent Application No. 08-203904 discloses a method for applying solder to a metallic bump by heating a protruding electrode of the core bump and bringing a solder sheet into physical contact with the heated electrodes. In this method, however, it is difficult to keep the amount of solder to be applied to the electrical connecting structure constant, so that unexpected joining between adjacent assemblies may occur. Finally, still further examples of various structures associated with solder formation or transfer are defined in U.S. Pat. Nos. 5,762,258 and 5,804,248.
One object of the present invention is to provide a method for forming an electrical connecting structure on an electronic component at relatively lower costs than many known processes while assuring an effective flip-chip form of attachment of the component.
Another object of the present invention is to provide a method for forming an electrical connecting structure to which a uniform amount of solder is applied even when the solder connections are spaced at a relatively narrow pitch.
A further object of the present invention is to provide a solder transfer plate which is to be used for forming such an electrical connecting structure.
According to one aspect of the invention, there is provided a method for forming an electrical connecting structure on an electronic component comprising the steps of forming a core bump on an electrode of an electronic component, forming at least one recess in a solder transfer plate, filling the recess with solder which contains metal different from the metal forming the core bumps, joining the electronic component to the solder transfer plate so as to bring the core bump into contact with the solder in the recess, and transferring the solder filled in the recess to at least a part of the core bump by separating the electronic component from the solder transfer plate.